Put the apples in a saucepan with 150ml of water and a tablespoon of the sweetener. Bring to the boil over a high heat, reduce the heat to low and cook for 10 minutes or until tender.
Transfer the apples to a food processor and blend until smooth. Sieve the mixture into a bowl, stir in the lemon juice and set aside to cool.
Whisk the egg whites until soft peaks form then whisk in the remaining sweetener until the mixture is shiny and stiff.
Carefully fold the egg whites into the apple mixture until well combined then spoon into chilled dessert glasses or bowls.
Chill for 2-3 hours and decorate with apple slices and mint sprigs to serve.